Technical Abstract:
The objective of this study was to determine sorption coefficients (Kd) in field-moist or unsaturated soils, using supercritical fluid extraction (SFE) and accelerated solvent extraction (ASE) techniques. SFE was performed using low density (i.e., 0.25 g mL-1) supercritical carbon dioxide, to remove pesticides from the soil water phase only, thus allowing gcalculation of sorption coefficients at low water contents. Soil water content and temperature affected sorption. Kd values for linuron, triadimefon, and metsulfuron methyl increased with increased water content, and decreased with increased temperature. An automated extraction system using ASE was developed. The ASE application used conditions comparable to batch equilibrium systems (0.01 M CaCl2 at 25 C) in order to desorb pesticides from soil and determine sorption coefficients. ASE was showed to be a fast alternative to the batch method for triadimefon and amitrole. The eapplications of using SFE and ASE to determine sorption coefficients allow studies on the influence of different realistic soil moisture levels on sorption behavior, studies that are impossible to perform with conventional batch techniques. This should give a more accurate overall perspective of pesticide fate in the field, than by sorption characterized by the batch method.